The PRESCP process originally developed by the principal investigator for impregnating telephone poles with preservative was found to be ideally suited for obtaining tree sap in quantity from which extracts could be prepared by evaporation. The process consists in fitting a pressure-tight cap on the end of a freshly-cut tree stem and pumping hot water into the cap. The sap displaced out of the other end is collected and evaporated to dryness to obtain the extract. 1967-'71: Extracts of 544 North American tree species were prepared and tested in the cancer screen. 31 showed confirmed activity against P388-lymphocytic leukemia. 1972-date: Extracts of 1238 tropical American species have been prepared and of 1000 tested so far, 152 show confirmed activity against P388. The significance of this work is evident when the number of confirmed actives found, 5.7% for North American and 15.2% Costarican, is compared with the results obtained from the same tree species by conventional methods of extract preparation. These yield less than 1% confirmed actives. It is proposed to continue this search for extracts active against cancer utilizing the information so far collected as a guide for more selective screening since it has been found that certain genera yield much higher percentages of actives than others.